In general, various gas reaction apparatuses for forming films on a substrate or etching the substrate have been used as semiconductor manufacturing apparatuses. Typically, such a gas reaction apparatuses includes a gas supply unit, a hermetic gas reaction chamber supplied with a gas from the gas supply unit, an exhaust route connected to the gas reaction chamber and an evacuation device, such as a vacuum pump or the like, connected to the exhaust route.
Such gas reaction apparatuses suffer from a problem that reaction by-products are solidified from the exhaust gas discharged out of the gas reaction chamber and are accumulated in the exhaust route or the evacuation device, which may lead to clogging of the exhaust route or failure of the evacuation device. Taking this into account, an exhaust trap device is arranged midway of the exhaust route to perform the task of trapping the reaction by-products present in the exhaust gas (see JP8-13169A, JP8-24503A and JP8-299784A, for example). Most frequently used as such kind of exhaust trap device is a collision-type cooling and trapping device in which collision plates, such as baffle plates, fins or the like, are arranged within a casing in an intersecting relationship with respect to a flow direction of the exhaust gas. The device is constructed such that, as the exhaust gas collides against the collision plates and is subjected to cooling, given kinds of solidified substances can be accumulated on the surface of the collision plates. In this collision-type cooling and trapping device, the shape and arrangement of the collision plates is optimized so as to increase trapping efficiency, thereby reducing outflow of the solidified substances toward a downstream side of the device.
Also proposed are exhaust trap devices each having a plurality of exhaust trap sections arranged in series along an exhaust route (see JP10-73078A, JP2000-256856A, JP2001-131748A and JP2001-329367A, for example). Examples of such exhaust trap devices include a device that, by employing a plurality of serially arranged exhaust trap sections whose cooling temperatures differ from one another, can increase trapping efficiency or can allow the respective exhaust trap sections to trap different kinds of solidified substances (JP10-73078A, JP2000-256856A and JP2001-329367A) and a device that can improve maintainability by distributing the accumulation of solidified substances over a plurality of exhaust trap sections (JP2001-131748A).
In the collision-type cooling and trapping device referred to above, the exhaust gas introduced into the device through a gas inlet port makes contact with the collision plates within an exhaust path and is rapidly cooled down. For this reason, the reaction by-products are adhered to around the gas inlet port in large quantities and the exhaust path shows a reduced conductance. This makes it impossible to keep the gas reaction chamber arranged at the upstream side in a vacuum condition or causes clogging in the vicinity of entrance of the exhaust path, which in turn poses a problem that the exhaust trap device needs to be maintained at an increased frequency.
To avoid such a problem, there is a need to raise the cooling temperature in the exhaust path. However, if the temperature in the exhaust path is raised, the reaction by-products cannot be sufficiently trapped in the exhaust trap device and the reaction by-products are solidified in an evacuation device or a scrubber arranged at the downstream side of the exhaust trap device, which causes a shortened maintenance cycle or a failure of the evacuation device or a scrubber.
The trap device disclosed in JP2001-131748A includes a plurality of trap members arranged in multiple stages along a flow direction of the exhaust gas and also divided into multi-groups; heating units for independently heating the respective groups of trap members, excepting for the group of trap members positioned downstreammost in the flow direction of the exhaust gas; and a heat quantity controller for controlling the amount of heat generated by each heating units. This ensures that the reaction by-products are accumulated first on the downstreammost trap member and then on the upstream side trap members in sequence, thereby avoiding uneven distribution in the amount of accumulation of the solidified substances on the plurality of trap members. With this trap device, however, the heating units are required to be controlled in a time-dependent manner, which makes a control unit complicated, and further the control needs to be performed in a highly sophisticated fashion depending on the constituents of the exhaust gas. In addition, since above-noted structure is primarily focused on the avoidance of uneven distribution in the amount of solidified substances accumulated within the trap device, the device suffers from a drawback in that it is difficult to reduce the amount of reaction by-products solidified at a more downstream side than the downstreammost trap member.